1. Field of the Invention
The present invention relates to waterproof electronic equipment that can preferably be used as in-vehicle electronic control equipment provided in an engine room or the like, for example, and an assembly method thereof.
2. Background of the Related Art
In in-vehicle electronic control equipment, a waterproof control unit having a connecter housing and a cover fixed to a circuit board as separate structures in which the circuit board is water-tightly held by a base as the first part of a casing, the cover as the second part of the casing, and an end lid as the third part of the casing integrally molded with the connector housing, with the end surface of the connector housing provided on one side of the circuit board exposed to the outside is known. This type of waterproof control unit is more suitable for standardization of the connector part than the form in which the connector housing and the cover are integrally molded, however, the unit requires waterproof structures between the cover and the end lid and between the end lid and the base in addition to the waterproof seal structure between the cover and the base.
For example, in a box-shaped control unit including a base having a rectangular shape with a bottom in which four side peripheral walls are stood from a bottom plate and the end surface side of the peripheral walls is opened, a circuit board having a rectangular shape on which electronic components are mounted and provided at the opening side of the base, and a cover having a lid part covering the electronic components of the circuit board and a flange part formed in contact with a peripheral edge part of the circuit board on the lid part, in the base, amount in contact with a rear surface of the circuit board when a sealing gap for allowing a seal material to intervene between the end surface of the peripheral walls of the base and the flange part of the cover is secured is provided, and the seal material is provided in the sealing gap under the condition that the circuit board is brought into contact with the mount and the circuit board is covered by the cover (for example, see JP-A-2003-258451 (Abstract, FIG. 3)).
In the above described related art, the circuit board is sandwiched between the step part of the base separately provided inside of the outer peripheral seal part and the flange part of the cover, and thus, there is a problem that, while the area of the circuit board becomes smaller, when it is desired to attach a component with heat generation having a relatively high dimension to the rear surface of the circuit board, it is difficult to obtain a sufficient height dimension. This is because the area of the printed board becomes smaller by the amount of the area of the stepped surface provided inside of the seal surface and the printed board comes closer to the inner bottom surface of the base by the amount of the lowered step dimension. Further, the sealing gap is adjusted by the height of the planar projection as the mount of the periphery of the circuit board, however, actually, the sealing gap is determined by the height of the contact surface of the attachment screws for tightening the base and the cover together, and, for adjustment of the sealing gap by the height of the planar projection of the base, it is necessary to provide a gap around the contact surface of the attachment screws and a problem that the attachment screws remain incompletely fastened and the screws easily become loose arises. On the other hand, if the contact surface of the attachment screws is first brought into contact and then the screws are reliably be fastened, a problem that the sealing gap becomes nonadjustable and may be more than the gap determined by dimension variations of the respective parts.